Silencer with frequency separating and modulating baffle

ABSTRACT

An air exhaust silencer comprises a housing having an inlet and an outlet with opposed porous dome shaped noise reducing members and a porous frequency separating and modulating baffle disposed within and between said noise reducing members, contoured and of such undulating shape and form extending into at least one of said dome shaped members so as to have a total surface area in excess of the cross sectional area of opening between said dome shaped members, for reducing and modifying high pressure sound frequencies and reducing back pressure.

United States Patent i Blatt et al. 1451 July 11, 1972 54] SILENCER WITHFREQUENCY 2,122,086 6/1938 Chase 1 a 1/70 SEPARATING AND MODULATIN2,218,063 10/1940 Munzer ..181/63 RAFFLE FOREIGN PATENTS OR APPLICATIONS[721 fizr gf 'r fg m gym 412,277 11/1966 Switzerland ..181/60 s Mich4809 Primary Examiner-Robert S. Ward,Jr. [22] Filed: Sept. 10, 1971Attorney-Daniel G. Cullen et a1. [21] App]. No.: 179,284 [57] ABSTRACTAn air exhaust silencer comprises a housing having an inlet [52] U.S.CI. 11881571], and an outlet with opposed porous dome shaped noise reducs1 1 1111 c1 F0ln1/10 F0111 7/16 F6111 7/18 i membu? and f'eqmncy [58]Fieid 181/60 68 70 56 36 A mg baffle disposed within and between saldnoise reducmg A members, contoured and of such undulating shape and formextending into at least one of said dome shaped members so as to have atotal surface area in excess of the cross sectional [56] ReferencesCited area of opening between said dome shaped members, for UNITEDSTATES PATENTS reducing and modifying high pressure sound frequenciesand reducing back pressure. 938,101 10/1909 Winters ..181/70 2,019,74611/1935 Tatter ..l81/61 6Claims,5DrawingFigures PATENTEDJUL 11 m2 3. 675734 sum 1 or 2 FIG. I

INVENTORS LELAND FRA s emf BY Qumifm";

ATTORNEYS PATENTEDJUL 1 1 I972 3 675 734 SHEET 2 CF 2 FIGS FIG.4

INVENTORS LELAND FRANCIS BLATT mwzwm ATTORNEYS SILENCER WITH FREQUENCYSEPARATING AND MODULATING BAFFLE RELATED INVENTION The present inventionis an improvement over the exhaust silencer shown in copending patentapplication Ser. No. 81,051 filed Oct. 15, 1970.

BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates tosound absorbing devices and more in particular to a noise subduingdevice to maintain a specific noise level within acceptable limits.

Almost universally, every thing, substance or matter moving provides orproduces noise at varying frequencies and at dif ferent noise levelswhich may range from a low frequency whisper to high frequency squeals.

Any consistent sound at whatever noise level is, in most cases, annoyingto the human ear, although the sound level may not be as high as toproduce a health hazard. However, in connection with machinery, whetherit be mechanical, electrical or fluid power operated or by combustion,noises are produced which, in instances, exceed a safe level,particularly at high frequencies.

It is known in the industry that the federal government establishedindustrial safety standards by the provision of the Walsh-Healey Actwhich was amended on May 8, 1969, in regard to occupational noiseexposure, setting a standard providing that a person may not work morethan 8 hours at a maximum 90 dBA (90 decibels measured on the A-scale ofa sound level meter).

Many noises produced in a plant or similar working place, areconsiderably higher than 90 dBA. Most of these noises are not merelypure tones, but in most cases are a combination of sounds and may rangefrom a low frequency roar to a high frequency squeal. Obviously,combined frequencies require differentiating of materials inside thesilencer to stop or absorb those frequencies or separate thosefrequencies in order that they not be added or combined with one anotherto produce a sound level unacceptable or unhealthful to human beings.Another factor to be considered is the power level of the sound field.Thus, if a great deal of noise is being produced at differentfrequencies, or the level of power is high, it would require extremelylarge and complicated silencers to reduce the noise to within atolerance acceptable to a human being at a certain distance from theorigin of the sound.

As mentioned before, sound is producted by matters or substances flowingor moving through the air or through another substance and the noiselevel of the sound is dependent on the pressure and speed of movement ofthe moving substance and the relative resistance of the matter or othersubstance through which the moving substance passes. Thus, air flowingthrough the orifice or venturi of an exhaust valve at relatively highspeed and pressure, creates a high frequency squealing sound, whereas,for instance, the sound produced inside of air operated tools is muchmore subdued, but this sound is combined with the noise created by theworking parts of the tool. Thus, these two examples require differenttypes of sound absorbing material for effective silencing to within asafe level.

Considerable difficulties are experienced in moderating or absorbingthese sounds created by the exhaust of pneumatic valves, motors andother air operated tools in the industry. Noise is also produced by thesound of mechanical movement of the working parts of the tools coupledwith other frequencies caused by air vibrations as air travels through aparticular valve or pneumatic motor.

It is known to the men skilled in the art of noise reduction orabsorbtion that, when the daily noise exposure is comprised of two ormore periods of noise, the different level and combined effect should beconsidered rather than the individual effect of each.

Most air tool and/or air valve applications, where a great deal of airflow is present, require the design of silencer chambers to be of utmostconsideration so as not to create excessive back pressure within thetool or valve which will cause a slowdown in the cycle of the operationtime.

Accordingly, the present invention provides an improved air exhaustsilencer construction adapted to effectively reduce high noise levels toa safe level not exceeding dBA.

The definition of the word sound depends on the point of view adopted.Subjectively, it may be regarded as a variation in a normal atmosphericpressure caused by vibrations or other pressure disturbances that aretransmitted to the human hearing mechanism causing a knowing sensation.The variation in a normal atmospheric pressure that is a part of thesound wave may be characterized by the rate in which such as thestandard musical tone a" occurs when a pressure change through acomplete cycle is 440 times per second.

The apparent loudness that we attribute to a sound varies not only withthe sound pressure but also with the frequency or pitch of the sound.The frequency being of a wave length which is within the frequency ofthe human ear is classified as sound.

Scientists and engineers have investigated many aspects of mans reactionto sound. The human ability to distinguish sound has been establishedbetween the frequency of 20 to 20,000 hertz. Most individuals can heartones in the frequency range of 200 to 10,000 hertz, even though thelevels are low. Within this frequency range, if the sound pressure levelis above 90 decibels, the Walsh-Healey Act as amended for occupationalnoise hazards, limits the individuals working time to 8 hours at 90decibels. Also, the law sets forth curves between and 8,000 hertz asbeing the frequency most likely to be injurous or affect the humanhearing. The upper limit at which we can hear airborne sounds depend onthe condition of our hearing and the intensity of the sound. The upperlimit is somewhere between 16,000 and 20,000 hertz.

Psychologists have found that certain sound frequencies are moreannoying and tiring to the human than other frequencies within the humanrange and it therefore becomes necessary for persons working on theecology of sound to be able to lower or destroy the frequencies causedby the noise and jumble of sounds created by moving machinery, escapingexhaust air, etc., that may be encountered and now considered anoccupational hazard.

Alternating sounds bear a closes resemblance to alternating electricalcurrents or light waves. Even though light travels at a fantastic speedof 186,000 miles per second while sound travels approximately 1 100 feetper second at sea level. There is analogy between the two which suggeststhe use of lenses of certain types to bend or change the frequency ofthe sound waves so that they may be destroyed or dispersed through thesilencer not to be impinged on the human working within the effectedarea.

In copending application Ser. No. 81,051 filed Oct. 15, 1970, thefrequency modulating baffle 74 does perform a function of blockingcertain frequencies, yet its minimum cross sectional area is not thebest conceivable design to change or filter out or cause interference ofsound waves of a specific frequency within the range most affecting thehuman hearing mechanism.

Furthermore, it is readily seen that the cross sectional area of bafi'le74 does not correspond or is not as great as the cross sectional area ofeither of the hemispherical chambers. If exhaust air pressure of 80p.s.i. is released at port 50, it would be restricted or cause a backpressure in the first chamber, restricting the exhaust time or slowingthe air flow through the silencing unit.

To overcome this, it is an object of the invention to provide a designof several center lenses. This sound lens may be constructed withvarious angles or curves not only increasing the cross sectional areaand reducing back pressure, but in such a manner when properlycalculated will destroy a certain high pressure frequency affecting thehuman hearing mechanism with no apparent loss in air flow efficiency.

These and other objects will be seen from the following specificationand claims in conjunction with the appended drawings:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal cross sectionthrough the present improved sound silencer with one form of frequencyseparating and modulating baffle.

FIG. 2 is a similar view of a modification thereof.

FIG. 3 is a similar view with another modification of the said bafile.

FIG. 4 is a similar view with still another form of baffle construction.

FIG. 5 is a right end view of any of the FIGS. 1 through 4.

The silencer 44 in FIG. 1 comprises a barrel type housing 46 closed atone end by a front end cap 48 having a threaded inlet opening 50 forattachment of the silencer to the noise or sound producing apparatus.

The interior of the housing 46 defines a chamber 52 in which is disposeda first dome shaped member 54 whose dome section 56 extendssubstantially the full length through the chamber. The open end of thedome shaped member 54 is directed away from the inlet opening 50 and isprovided with a radial flange 58 by which the member 54 is retained inthe housing 46 by abutment against inner radial shoulder 60 of thehousing. Thus, the closed front end 57 of the dome shaped member 54 isdisposed adjacent inlet opening 50 in axial alignment therewith.

The silencer 44 is provided with a second dome shaped member 62 which isidentical to the first dome shaped member. The second dome shaped memberis positioned in opposite direction to the first dome shaped member sothat the closed dome portion 64 extends outwardly of the housing 46. Theopen end of the dome shaped member 62 is similarly provided with aradial flange 66 disposed within the rear end of the housing in abuttingrelationship against flange 58 of the inner dome shaped member. Thesecond dome shaped member is retained in the rear end of the housing bymeans of a lock ring 68. A sealing member 70 is disposed between theadjoining flange portions 58 and 66 and the inner surface of thehousing. The dome shaped members are preferably made of sintered bronzeof a defined micron size suitable for the particular application inwhich the silencer is used.

The members 54 and 62 act as frequency distorters and, due to theexpanded dome shaped portions, provide a greatly increased soundabsorbing area with a minimum of material. The combined dome shapedmembers 54 and 62 provide a sound absorbing chamber 72 of a relativelylarge area which is divided by a baffle member 74 in the form of a plateretained between the adjoining flange portions 58 and 66. The bafflemember 74 can be made of felt, screening, perforated metal, urethane, orother porous material, depending on the type of sound or noise to beabsorbed. The baffle member 74 acts as a frequency variation separatorto screen different sounds received by the silencer according to theirfrequency.

The present porous frequency separating and modulating baffle 74 is oneillustration of a design for the destruction of certain specifiedfrequencies having a relation to the cross sectional area between thehemispherical dome shaped sound silencing members 56 and 64.

The present baffle includes an annular retaining flange 76 interposedbetween flanges 58 and 66 and inwardly thereof is irregularly shaped andcontoured with a series of curved and/or angularly related surfaceswhich extend into at least one if not both of the dome shaped members tothus produce a greatly enlarged surface area compared to the crosssectional area between the dome shaped members.

Also this increased surface area for the transmission of mediumtherethrough is considerably large compared to the total interiorsurface area of the opposed dome shaped members. For illustration, andas an example in FIG. 1, the total surface area of the dome shapedmembers is 13.647 square inches. The surface area of the bafile member74 is approximately 6.378 square inches.

It is noted with respect to FIG. 2 that the comparative surface area ofthe baffle member has been increased by modifying the proportions so asto have an area of approximate 8.470 square inches.

With respect to FIG. 1 the present bafile 74 includes an annular coneshaped portion 78 and coaxially thereof and forming in a continuation isthe oppositely directed cone shaped portion 80 with the connectingcontinuous curved areas shown at 82. Thus, the baffle 74 defines thethree chambers A, B, C to thus provide a surface area through which themedium must flow which is greatly increased with respect to the crosssectional area between the opposed cone shaped members.

Referring to FIG. 2 the construction is substantially the same exceptthat the angular surfaces are different and therefore affect differentfrequencies. Here the frequency separating and modulating baffle 84 hasan increased surface area as above described in view of the elongatedannular converging surface portions 86 and the oppositely extendingcontinuation or elongated cone shaped portion 88 with connecting curvedportions 90 to thus define the differently shaped chambers D, E, and F.

A slightly modified curvature or form of frequency separating andmodulating bafile is designated at 92, FIG. 3, which consists of aseries of oppositely arranged or curved or undulating surfaces 94, 96and 98, all interconnected to define the chambers G, H. and I.

It is noted with respect to FIGS. 1, 2 and 3 that the formed continuousportions of the baffle 74, 84 and 92 extend respectively into thecorresponding dome shaped members to thus provide for increased surfacearea for the passage of the flow medium therethrough. In this particularconstruction shown in FIG. 3, the surface area is less than that shownin FIGS. 1 and 2 with the result that there is a greater resistance toflow and, accordingly, a higher back pressure developed than in theembodiments shown in FIGS. 1 and 2.

A modified form of bafile 100 is shown in FIG. 4 and wherein the centralportion of said baffle is concave-convex at 102 and extends into one ofthe dome shaped members. Here again, back pressure created due to thissurface area is greater than that created in FIG. 3 or in any of theother illustrations, FIGS. 1 and 2, where greatly increased surfaceareas are provided due to the curved and angular lens like or irregularcontoured surfaces.

The present irregularly shaped frequency modulating baffle may thus bedesigned for the destruction of certain predetermined frequencies thatmay be produced within a particular chamber having a plurality ofdifierent noise sources when it is desired to destroy or reduce thesewithout creating back pressure or in providing for modified backpressure in accordance with the particular design of baffle.

The foregoing illustrations, FIGS. 1 through 4, merely show severalpreferred embodiments of the irregularly shaped sound or frequencyseparating and modulating baffle and wherein the total surface area issubstantially increased due to its irregular shape.

While sintered bronze has been referred to in the illustrativeembodiments of the invention, other materials which would be regarded asequivalent thereto include sintered steel, porous porcelain or stone orporous plastic materials.

Having described the invention, reference should now be had to thefollowing claims:

1. A silencer adapted to reduce the combined noise level of a flowmedium and working mechanism normally above 90 decibels to a sum totalvalue below 90 decibels comprising:

a housing having an inlet for passage of said flow medium into saidhousing and an outlet;

opposed dome shaped porous first and second noise reducing members withtheir open ends in abutting relation, forming a chamber in between them;

said first noise reducing member having surfaces disposed adjacent saidinlet for passage of said flow medium into said chamber, and said secondnoise reducing member having surfaces extending from the housing outletdefining an outlet for passage of said flow medium from said chamber toatmosphere, so that the noise level of said flow medium as it passesthrough said first and second noise reducing members is substantiallyreduced, and

a porous frequency separating and modulating bafile disposed betweensaid first and second dome shaped members within said chamber, having anannular flange retained between abutting outer portions of said domeshaped members, and inwardly of said flange irregularly shaped contouredportions extending into at least one of said dome shaped members andhaving a total surface area greater than the maximum cross sectionalarea between said dome shaped members for reducing and modifying highpressure frequencies and reducing back pressure.

2. In the silencer of claim 1, the contoured portion of said frequencymodulating baffle including a pair of continuous concentric oppositelyarranged coned shaped members extending into both dome shaped members.

3. In the silencer of claim 1, the contoured portion of said frequencymodulating baffle including an outer annular converging portion at itssmallest diameter terminating in an oppositely arranged cone shapedportion.

4. In the silencer of claim 1, the contoured portion of said frequencymodulating baffle including a series of continuous undulating curved andangularly related surfaces.

5. In the silencer of claim 1, the contoured portion of said frequencymodulating baffle including a series of continuous oppositely arrangedconcave-convex portions.

6. In the silencer of claim 1, the contoured portion of said frequencymodulating baffle including a central concave-convex portion.

1. A silencer adapted to reduce the combined noise level of a flowmedium and working mechanism normally above 90 decibels to a sum totalvalue below 90 decibels comprising: a housing having an inlet forpassage of said flow medium into said housing and an outlet; opposeddome shaped porous first and second noise reducing members with theiropen ends in abutting relation, forming a chamber in between them; saidfirst noise reducing member having surfaces disposed adjacent said inletfor passage of said flow medium into said chamber, and said second noisereducing member having surfaces extending from the housing outletdefining an outlet for passage of said flow medium from said chamber toatmosphere, so that the noise level of said flow medium as it passesthrough said first and second noise reducing members is substantiallyreduced, and a porous frequency separating and modulating baffledisposed between said first and second dome shaped members within saidchamber, having an annular flange retained between abutting outerportions of said dome shaped members, and inwardly of said flangeirregularly shaped contoured portions extending into at least one ofsaid dome shaped members and having a total surface area greater thanthe maximum cross sectional area between said dome shaped members forreducing and modifying high pressure frequencies and reducing backpressure.
 2. In the silencer of claim 1, the contoured portion of saidfrequency modulating baffle including a pair of continuous concentricoppositely arranged coned shaped members extending into both dome shapedmembers.
 3. In the silencer of claim 1, the contoured portion of saidfrequency modulating baffle including an outer annular convergingportion at its smallest diameter terminating in an oppositely arrangedcone shaped portion.
 4. In the silencer of claim 1, the contouredportion of said frequency modulating baffle including a series ofcontinuous undulating curved and angularly related surfaces.
 5. In thesilencer of claim 1, the contoured portion of said frequency modulatingbaffle including a series of continuous oppositely arrangedconcave-convex portions.
 6. In the silencer of claim 1, the contouredportion of said frequency modulating baffle including a centralconcave-convex portion.